<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        body{
            height: 3000px;
        }
        #backTop{
            width: 80px;
            height: 80px;
            background: blueviolet;
            position: fixed;
            right: 50px;
            bottom: 80px;
            display: none;
            text-align: center;
            line-height: 80px;
            cursor: pointer;
        }
    </style>
</head>
<body>
<div id="backTop">Top</div>
</body>
</html>
<script src="js/jquery-1.10.1.js"></script>
<script>
    $(function () {

        $(window).scroll(function () {
            if($(window).scrollTop() > 200){
                $("#backTop").fadeIn();
            }else{
                $("#backTop").fadeOut();
            }
        })

        $("#backTop").click(function () {
            $(window).scrollTop(0);
        })
    })
</script>